1. Field of the Invention
The present invention relates to an image processing apparatus and method, and more particularly to an image processing apparatus and method for performing an image processing including control of a total toner amount.
2. Description of the Related Art
Generally, an image forming apparatus such as a printer has a structure as shown in FIG. 6. As shown in FIG. 6, an image forming apparatus 100 is comprised of a job receiving section 101, a job management section 102, an image processing section 103, and an output processing section 104.
The job receiving section 101 receives a print job which is issued by an information processing device such as a personal computer. The job management section 102 holds the job received by the job receiving section 101 and manages its execution sequence. The image processing section 103 executes an image processing of image data included in the job, of which execution is instructed by the job management section 102, in accordance with the image data and the output processing section 104. The output processing section 104 forms an image on paper with toner on the basis of the image data which has undergone the image processing executed by the image processing section 103.
Here, the image processing section 103 will be described in detail. FIG. 7 is a block view showing a functional structure of the image processing section 103. As shown in FIG. 7, the image processing section 103 is comprised of a color conversion unit 111, a black generation unit 112, a gradation correction unit 113, a total toner amount control unit 114, and a screen processing unit 115.
The color conversion unit 111 converts image data RGB (in) indicated by individual colors R (Red), G (Green) and B (Blue) included in a job to image data CMY (0) which is indicated by individual colors C (Cyan), M (Magenta) and Y (Yellow). This conversion employs, for example, a DLUT (Direct Look Up Table). In the notations RGB (in) and CMY (0) indicating the image data in the drawing, the characters in parentheses are symbols used for the sake of discrimination from other image data.
The black generation unit 112 converts the image data CMY (0) to image data CMYK (0) indicated by individual colors C, M, Y, and K (Black). The processing by the black generation unit 112 is performed by performing a processing for replacing under colors indicated by CMY called as the UCR (Under Color Removal) with color K.
The gradation correction unit 113 conducts gradation correction of the image data CMYK (0), and outputs the corrected image data CMYK (1). In a case where the image data contained in the job is CMYK-based image data CMYK (in), the image data CMYK (in) is inputted to the gradation correction unit 113. The correction to be effected by the gradation correction unit 113 is made in accordance with the characteristics of the output processing section 104, and a TRC (Tone Reproduction Curve) is used to improve color reproducibility in the output processing section 104.
In a case where the output processing section 104 forms an image on the basis of the image data CMYK (1) and the total toner amount exceeds the ability of the output processing section 104, the total toner amount control unit 114 converts the image data CMYK (1) to image data CMYK (2) of which total toner amount is suppressed. The toner amount to be placed on paper by the output processing section 104 is limited because of its ability. Therefore, when the image data CMYK (1) is used as it is, there is a possibility that a total amount of the individual color toners exceeds the limitation. For example, when it is assumed that a maximum value of the toner amounts of the individual colors is 100%, the total toner amount becomes 400% at most. Meanwhile, when it is assumed that a maximum total toner amount which can be processed by the output processing section 104 is 240%, it is apparent that there is a possibility that the total toner amount exceeds 240%. In this case, the total toner amount control unit 114 generates the image data CMYK (2) which has the image data CMYK (1) corrected such that the total toner amount becomes 240% or less.
The screen processing unit 115 performs a screen processing of the image data CMYK (2), generates image data CMYK (out), and outputs the generated image data CMYK (out) to the output processing section 104.
It should be noted that a structure similar to the structure of the image processing section 103 described here is described in Japanese Patent Application Laid-Open No. 9-37094.
Then, an image processing section 103′ having a structure different from that of the image processing section 103 will be described. It should be noted that the image processing section 103′ can be used instead of the image processing section 103 used in the structure shown in FIG. 6.
FIG. 8 is a block view showing a functional structure of the image processing section 103′. As shown in FIG. 8, the image processing section 103′ is comprised of a color conversion unit 121, a black generation unit 122, a total toner amount control unit 124, and a screen processing unit 126.
The color conversion unit 121 converts image data RGB (in) which is indicated by individual colors R, G and B included in a job to image data CMY (0) which is indicated by individual colors C, M and Y. This conversion employs, for example, a DLUT (Direct Look Up Table). In the notations RGB (in) and CMY (0) indicating the image data in the drawing, the characters in parentheses are symbols used for the sake of discrimination from other image data.
The black generation unit 122 converts the image data CMY (0) to image data CMYK (0) which is indicated by individual colors C, M, Y and K. The processing by the black generation unit 122 is performed by performing a processing for replacing under colors indicated by CMY called as the UCR (Under Color Removal) with color K.
In a case where an image is formed by the output processing section 104 on the basis of the image data CMYK (0) and its total toner amount exceeds the ability of the output processing section 104, the total toner amount control unit 124 converts the image data CMYK (0) to image data CMYK (1) of which total toner amount is suppressed. And, when the image data contained in a job is CMYK-based image data CMYK (in), the image data CMYK (in) is input to the total toner amount control unit 124.
The screen processing unit 126 performs a screen processing of the image data CMYK (0) or the image data CMYK (1), generates image data CMYK (out), and outputs the generated image data CMYK (out) to the output processing section 104. And, the screen processing unit 126 also performs gradation correction in accordance with the characteristics of the output processing section 104 at the time of the screen processing.
Incidentally, the configuration in that the gradation correction is performed by the gradation correction unit 113 as in the image processing section 103 shown in FIG. 7 has a possibility that the image quality of an outputted image is degraded in comparison with the configuration in that the gradation correction is performed by the screen processing unit 126 in the image processing section 103′ shown in FIG. 8.
For example, when it is assumed that the gradation correction is performed by the gradation correction unit 113 using a TRC shown in FIG. 9A, both image data having a value (input value) 127 and image data having a value (input value) 128 are converted to image data having a value (output value) 60. It results from the precision of the TRC, and under normal circumstances, the individual image data must be originally converted to image data having values (output values) 59.5 and 60.4 respectively. But they are converted to image data having a value (output value) 60 because of the precision of the TRC. In other words, it means that there is no gradation between the image data having the value (input value) 127 and the image data having the value (input value) 128.
As a result, even if the screen had 256 gradations or more, the image to be outputted is an image having less than 256 gradations. For example, the screen shown in FIG. 9B can have one pixel divided to eight, and a total number of gradations is 256 (32×8).
Meanwhile, in a case where gradation correction is performed by the screen processing unit 126 in the image processing section 103′, both the image data CMYK (0) and the image data CMYK (1) to be inputted to the screen processing unit 126 have 256 gradations because the gradation correction is not performed in a previous stage of the screen processing unit 126. And, if the gradation correction of the image data having the value 127 results in a value 59.5, the image has 14+⅞(59.5× 2/8) pixels lighted when the value 59.5 is normalized to a screen size as shown in FIG. 9C. And, if the gradation correction of the image data having the value 128 results in a value 60.4, the image has 15+⅛(60.4× 2/8) pixels lighted when the value 60.4 is normalized to a screen size as shown in FIG. 9D. Thus, there is a difference in gradation between the above images.
The above-described configuration in that the gradation correction is performed by the gradation correction unit has a possibility that the image quality of the output image is deteriorated in comparison with the configuration in that the gradation correction is performed by the screen processing unit.
And, the configuration in that the total toner amount is controlled by the total toner amount control unit 124 prior to the gradation correction (by the screen processing unit 126) in the image processing section 103′ shown in FIG. 8 has a possibility that the image quality of the output image is degraded in comparison with the configuration in that the total toner amount is controlled by the total toner amount control unit 114 after the gradation correction by the gradation correction unit 113 in the image processing section 103 shown in FIG. 7.
For example, it is assumed that the total toner amount which can be processed by the output processing section 104 is 240%, and the image data CMYK (0) to be inputted to the total toner amount control unit 124 has a total amount of 320% with individual colors of 80%. Because the total toner amount of the image data CMYK (0) exceeds 240%, the total toner amount control unit 124 converts the image data CMYK (0) to image data CMYK (1) having a total amount of 240% with individual colors of 60%. This image data CMYK (1) is input to the screen processing unit 126, but there is a possibility that the total toner amount of the image data CMYK (out) to be outputted becomes smaller because the screen processing unit 126 performs the gradation correction. Generally, the total toner amount tends to become small by the gradation correction, and data of a total toner amount of 240% becomes, for example, data of a total toner amount of 160%. In other words, the total toner amount of the image data CMYK (out) to be outputted becomes 160%, and the mage is formed on the basis of the image data CMYK (out) having the total toner amount of 160% although the output processing section 104 has the processing ability of up to a total toner amount of 240%, resulting in degradation of its image quality.
Meanwhile, it is assumed that the total toner amount control is performed by the total toner amount control unit 114 after the gradation correction by the gradation correction unit 113, and image data CMYK (0) having a total amount of 320% with individual colors of 80% is inputted to the gradation correction unit 113. Then, image data of which total toner amount has become small by the gradation correction effected by the gradation correction unit 113, for example, image data CMYK (1) having a total amount of 280% with individual colors of 70%, is output from the gradation correction unit 113. And, this image data CMYK (1) has a total toner amount of exceeding 240%, so that the total toner amount is controlled by the total toner amount control unit 114. As a result, image data CMYK (2) having a total amount of 240% with individual colors of 60% is output. The processing ability of the output processing section 104 is a total toner amount of 240%, so that an image based on the image data CMYK (2) is formed by using the output processing section 104 up to the limit of its processing ability.
As described above, the configuration in that the total toner amount control is performed prior to the gradation correction has a possibility that the image quality of the output image is degraded in comparison with the configuration in that the total toner amount control is performed after the gradation correction.
As described above, according to the image processing by the image forming apparatus, the gradation correction is performed in compliance with the ability of the output processing section at the time of the screen processing, so that an output image having better gradation than that obtained when the gradation correction is performed prior to the screen processing can be obtained. Meanwhile, in a case where the total toner amount control is performed before the gradation correction, the total toner amount control cannot be performed appropriately, and there is a possibility that the image quality of the output image is degraded.
Accordingly, the present invention provides an image processing apparatus and method capable of performing an image processing that can perform appropriate total toner amount control even when the total toner amount control is performed prior to gradation correction.